The Autozone link no worky.
Anyway, I used one off a Ford Explorer. I have found that plate-and-fin coolers in the 18,000-20,000 gvwr range are a good fit and work well. Check out this thread
http://www.mx-3.com/phpbb2/viewtopic.php?t=36307 where it is talked about.
Pop the hood and look down at the tranny, you'll see two hoses coming out that both run to the radiator. The one on the left stays put. The one on the right gets pulled off. The two hoses on the tranny cooler get connected in place of this hose (one of the hoses from the tranny cooler goes to the tranny, the other goes to the radiator).
I have a few pictures in that link that shows how I mounted mine. A few dollars at Home Depot gets you all the hardware you need to mount the cooler behind the bumper. Use transmission cooler hose, DO NOT fuel hose or anything else that will fail a few months later. The hole operation will take you an hour, 2 if you are taking your time. There is a nice big gap around the driver side of the radiator to run the hoses. Use 5/16's hose. Secure them with zip-ties so they dont flop around.
If you havent changed the fluid and filter within the last 20,000 miles or so, now is a good time to do it. Use Dexron III/Mercon fluid.
"The answer is: More power. I dont care what the question is."
-Tim Allen